Oxazolidine-3-oxyl derivatives

ABSTRACT

Novel oxazolidine-3-oxyl compounds, wherein the two carbon of the oxazolidine ring is a carbon in the chain of palmitoleic acid, e.g. cis-2-(11-carboxy-3-undecenyl)-2-propyl-4,4diethyloxazolidine-3-oxyl, which are useful as spin labels for biological membranes, are prepared by reaction of a 2-amino-2lower alkyl-alkanol with an oxopalmitoleic acid, the resulting product oxidized to the corresponding oxazolidine-3-oxyl.

United States Patent McConnell et al.

June 6, 1972 'OXAZOLIDINE-l'i-OXYL DERIVATIVES Harden M. McConnell, Stanford; Edwin F. Ullman, Atherton, Calif.

Assignee: Synvar Associates, Palo Alto, Calif.

Filed: Apr. 17, 1970 Appl. No.: 29,661

Inventors:

US. Cl ....260/307 F, 23/230, 252/408 Int. Cl. ..C07d 85/26 Field of Search ..260/307 F References Cited OTHER PUBLICATIONS Keana et al., J. Am. Chem. Soc. 89, 3055-3056 1967).

Primary Examiner-Alex Mazel Assistant Examiner-R. V. Rush Attorney-Townsend & Townsend [57] ABSTRACT 5 Claims, No Drawings OXAZOLIDINE-Ci-OXYL DERIVATIVES This invention is directed to novel oxazolidine compounds. More particularly, this invention is directed to novel oxazolidine3oxyl compounds which contain diorgano substitution at the C position.

Specifically, the novel compounds of this invention are represented by the following formula:

wherein: R is hydrogen or lower alkyl,

R, and R are each a lower alkyl, R, is (a) CH (CH where m is -2, or I Y where p is 2-4, and R is where n is 24, or (b) (CH )q coon where q is 2-4. Specifically, when R3 is CH3 (CH2),,,, R, is

Similarly, when R is CH CH R is (CH COOH. The total number of carbon atoms m+n is 4 and p-l-q=6,i.e. the total number of carbon atoms contained in groups R;, and R is 15.

The compounds of this invention may alternatively be characterized as labeled palmitoleic acids, the acids substituted at one of the C -C or CQ-C methylene groups with an oxazolidine-3-oxyl. The carbon of the substituted methylene group forms part of, and is bonded to the nitrogen and oxygen atoms of the oxazolidine ring as illustrated below for a C substituted palmitoleic acid in which R is hydrogen.

)CH; CH3 (Us 0.

The oxazolidine may be positioned at any one of the C,-C,, or C -C carbon atoms. Depending upon the positioning of the oxazolidine relative to the palmitoleic acid double bond, the organic group to the left of the substituted carbon can be defined by either R (a) or R (b). Similarly, the organic group to the right of the substituted carbon atom can be defined by either R.,(a) or R (b). In the above illustration, the organic group to the left of the substituted carbon corresponds to R (a), the organic group to the right of the substituted carbon to R,,(a). g

The compounds of this inventionare useful as spin labels for biological membranes. The labeling process entails immersion of the membrane containing material (for example, nerve fibers, erythrocytes, etc.) in a buffer containing one of the above radicals. The ESR spectrum of the membrane demonstrates Incorporation of the label. Changes in the membrane structure resulting from a biochemical change will be reflected in a change in the ESR spectrum. Such novel compositions are especially useful for example, for determining the structure and properties of membranes, and the nature of chemical and physical processes involving same. A more complete discussion of spin label ESR techniques appears in United States application Ser. No. 496,622, now US. Pat. No. 3,489,522, and incorporated herein by a reference.

The compounds of the present invention may be prepared from the corresponding oxooleic acids by the general technique described in Keana et al., Journal American Chemical Society, 89,3055 (1967), incorporated herein by reference. By this method, a 2-amino-2-lower alkyl-lower alkanol is condensed with an oxopalmitoleic acid (a ketone) to give an oxazolidine which is subsequently oxidized with mchloroperbenzoic acid to the nitroxide radical. The reaction, illustrated for 2-amino-2-methyl propanol, proceeds in the manner as shown below:

NH N-O The reaction of oxopalmitoleic acid and amino alcohol is carried out in an organic solvent which is immiscible with water. Such solvents include benzene, cyclohexane, tetrahydrofuran, ether, chloroform, etc. The reaction is carried out in the presence of a catalytic amount of a strong acid such as H p-toluene sulfonic acid, hydrochloric acid, and the like. The reaction temperature may vary from 50-160 and depending upon the particular temperature selected, the time of reaction will vary from 1-48 hours. After reaction, water is separated by use of a drying agent or by distillation.

Suitable 2-arnino-2-alkyl alkanols in the above reaction include 2-amino-2-methyl butanol, 2-arnino-2-methyl propanol 2-amino-2-ethyl butanol, and the like. Also suitable are amino alcohols of the general formula:

where R is a lower alkyl and may be the same or different. For example, each of the Rs may represent a methyl group. Using an amino alkanol of this type of structure provides an oxazolidine-3-oxyl compound of this invention in which R of the general formula given above is a lower alkyl group.

Other suitable oxidizing agents in the oxazolidine oxidation include hydrogen peroxide with ether sodium tungstate or phosphotungstic acid catalyst. In general, any oxidizing agent can be used which can supply an oxygen atom. The oxidation reaction proceeds satisfactorily at room temperature and may take from less than a minute to several hours.

In essence, in the process employed in this invention, an oxo substituted palmitoleic acid is reacted with a 2-amino-2-lower alkyl-lower alkanol. The alkanol reacts with the acid through the 0x0 group; thereby forming an oxazolidine ring in which the 0x0 carbon atom of the palmitoleic acid is incorporated into the ring. The resulting product is then oxidized in the presence of a suitable oxidizing agent to form the 3-oxyl derivative.

The point of oxazolidine ring attachment is determined by the positioning of the 0x0 group, this dependence reflected in the alternative definitions of R and R To prepare any of the oxazolidine-Ii-oxyl derivatives within the scope of this inventlon, it is first necessary to' prepare an appropriately substituted oxopalmitoleic acid. The positioning of the oxo group can accordingly be regulated by selection of reactants used, and the nature of the reaction sequence chosen in the preparation of the acid. The oxopalmitoleic acids used in this invention can be characterized as belonging to one of two groups as set forth below, the groups differing only in the relationship of the unsaturated bond to the oxo radical.

wherein m is from to 2, n from 2 to 4, and m+n=4 in fonnula I; and p is from 2 to 4, g from 2 to 4 andp+q=6 in formula H.

A different set of reactions is required for each group. The preparation of these acids is set out in the following flow diagram.

EXAMPLE 1 (1) Preparation of l3-oxopalmitoleic acid (a) 12-Carbomethoxy-4-dodecynoic acid chloride 0 ClC (CHz)2CEC(CHz)7COOCHs lillAi'llUN HICU IHCNCE FUR PREPARATION OF OXOIALMITOLEIC ACIDS OF FORMULA I Reaction sequence for preparation of oxooleic acids of Formula ll.

CIOC(CH2)nCEC(CH2)7COOCH2 TB 1 l. of liquid ammonia is added 20 moles of sodium and a crystal of ferrous sulfate. After the blue color disappears l0 at/Eco CdCIz CICO(CH1)QCOOCH3 n i Pd on charcoal In the above reaction sequences the last two steps may be reversed. That is, the reduction of the triple bond of the acetylenic ester may proceed the hydrolysis step. it is also possible to postpone the hydrolysis step until afterthe introduction of the oxazolidine and its oxidation to a nitroxide radical.

The C -C alkynoic acid starting materials in the preparation of the oxopalmitoleic acids of formula I are commercially available, and may also be prepared by well-known techniques. The l-octyne starting material in the preparation of the oxooleic acids of formula II is similarly available.

The reactions depicted in the above-illustrated reaction sequences are all standard reactions, e.g. the substitution of OH with C1 by reaction with thionyl chloride. The suitable reaction conditions employed herein fall within the general conditions for these standard reactions. it should be appreciated that there is no real criticality in the process conditions. A wide range of conditions is possible. The preferred conditions for a given reaction can easily be determined by routine experimentation. Those reported in the illustrated preparations are typical. The reactants will generally be added in equimolar proportions. However, one reactant may be U mmoles of 4-pentynoic acid is added and the solution stirred II (b) 13-ox0-9-hexadecynoic acid CHJ(CH2)2C(CHz)2CEC(CH1)1CO0lI To the crude acid chloride obtained in the preceding experiment dissolved in 500 ml of dry benzene is added dropwise over 30 minutes a solution of 1 equiv. of dipropyl cadmium in 200 ml benzene which has previously been prepared from ethereal l-propylmagnesium bromide by the addition of 0.5 equivalent of cadmium chloride. After the addition is complete, the mixture is stirred at room temperature for one 'hour followed by warming to reflux for 15 minutes. The mix- O I] H H (e) 13-ox0pa1mitoleic acid H; (C H2 2C (0 Hz) 20:0 (0 H9 0 O O H The acid obtained in the preceding experiment is dissolved in ether and stirred under a hydrogen atmosphere with a catalytic amount of palladium on charcoal. After the uptake of one equivalent of hydrogen, the catalyst is removed by filtration and the solution evaporated to dryness. The product is crystallized from petroleum ether.

(11) Preparation of cis-2(1 1-carboxy-3-undecenyl)-2- O NH To a solution of the above obtained l3-oxopalrnitoleicacid in 50 ml of benzene is' added excess 2-amino-2-methylpropan l-ol and a trace of p-toluene sulfonic acid. The solution is heated at reflux and the water removed with a water separator. The solution is then cooled and washed several times with water, dried over sodium sulfate, and evaporated to dryness in vacuo. The oxazolidine residue is taken up in ether and the resulting solution cooled in an ice bath. To this stirred solution is added dropwise over 20 minutes 1.5 equiv. of mchloroperbenzoic acid. The mixture is then allowed to warm to room temperature. After standing for 24 hours the solution is washed with just enough cold 5% sodium bicarbonate to remove the m-chlorobenzoic acid. The organic solution is then evaporated to dryness and the oxazo1idine-3-oxyl recrystallized from methanol.

EXAMPLE 2 Alternatively, oxidation of oxazolidine prepared following the procedure of Example 1, is achieved by stirring the ox azolidine in a 50% ethanol-water solution containing a 20-fold excess of hydrogen peroxide and a few crystals of sodium metatungstate. After stirring for 2 days at room temperature, sufficient sodium carbonate is added to render the solution basic and the mixture is washed several times with ether, adjusted to pH 4 with phosphoric acid and repeatedly extracted with ether. The extracts are dried and evaporated to give the product radical. The above procedure is again repeated, substituting phosph otungstic acid as the oxidation agent, and obtaining the oxazolidine-3-oxy1.

EXAMPLE 3 (1) Preparation of 4-oxopalmito1eic acid (a) l-Chloro-S-dodecyne CH (CH C C(CH C1 To 1 l. of liquid ammonia is added 10 mmoles of sodium and a crystal of ferrous sulfate. After the blue color disappears, l0 mmoles of l-octyne is added and the solution is stirred for 30 minutes. l-Bromo-4-chlorobutane (l0 mmole) is then added dropwise over 15 minutes and stirring continued for an additional 2 hours. The solvent is then allowed to evaporate and the residue is partitioned between ether and water. The ether layer is dried and distilled to yield the chloroacetylene.

A solution of 1 equivalent of l-chloro-S-dodecyne in dry ether is stirred under nitrogen with 1 equivalent of magnesium metal. Afier nearly complete dissolution of the metal, 0.5 equivalents of dry cadmium chloride is added and the solution is evaporated to dryness in vacuo. Dry benzene is added to the residue, the resulting suspension filtered under nitrogen, and then added dropwise to a dry benzene solution of one equivalent of the acid chloride of monomethyl succinic acid ester. After the addition is complete (about 30 minutes), the mixture is stirred at room temperature for one hour followed by warming to reflux for 15 minutes. The mixture is then cooled and extracted successively with aqueous sodium carbonate, hydrochloric acid and water. The solvent is evaporated in vacuo and excess methanolic sodium hydroxide added. This solution is allowed to reflux for 15 minutes whereupon it is poured into water and extracted several times with ether. The aqueous solution is then acidified with hydrochloric acid and the product isolated by extraction with ether and evaporation of the extracts.

Following the procedure of Example 1, 4-oxopalmitoleic acid is reacted with 2-amino-2-methyl propanol, and the reaction product oxidized with m-chloroperbenzoic acid to yield the above named product.

EXAMPLE 4 Preparation of cis-2(1 1-carboxy-3-undecenyl)-2-propyl-4,4-

diethyl-oxazolidine-3-oxyl Following the method of Example 1, 13 oxopalmitoleic acid is reacted with 2-amino-2-ethyl butanol, and the resulting product then oxidized with m-chlorobenzoic acid to yield the named product.

wherein R is hydrogen; R, and R are each alkyl of one or two carbon atoms;

R, is (a) CH (CH where m is -2, or (b) ll ll (1'HKCHQACZJXCHQU where p is 2-4; and

R is

II II -(OHz)nC=c(cH, ,co0n,

where n is 2-4 or (b) (CH ),,COOH where q is 2-4; subject to the limitation that when R is CH (CH,),,,

R is -(CH,) COOH, and m n=4 and p+q=6.

2. An oxazolidine-Soxyl in accordance with claim 1 wherein R and R are each methyl.

3. The cis-2-( 2-carboxyethyl )-2-( 5-dodecenyl)-oxazolidine-3-oxyl of claim 2 wherein R, is

and R. is (CH,),COOH.

4. The cis2-( 13-carboxyl-5-tridecenyl)-2-methyl oxazolidine3oxyl of claim 2 wherein R is CH;,, and R is 5. The cis-2-( l 1-carboxy-3-undecenyl)-2-propyl oxazolidine3-oxyl of claim 2 wherein R is CH;,(CH and R is UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3 668 214 Dated June 6 1972 Harden M. McConnell et a1. Inventor(s) It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

The term of this patent subsequent to June 27, 1989, has been disclaimed.

Signed and Sealed this twenty-eight Day of 0ct0ber1975 [SEAL] A lies I.

RUTH C. MASON C. MARSHALL DANN Arresting Officer (ummissimzer ofParents and Trademarks 

2. An oxazolidine-3-oxyl in accordance with claim 1 wherein R1 and R2 are each methyl.
 3. The cis-2-(2-carboxyethyl)-2-(5-dodecenyl)-oxazolidine-3-oxyl of claim 2 wherein R3 is and R4 is -(CH2)2COOH.
 4. The cis-2--(13-carboxyl-5-tridecenyl)-2-methyl oxazolidine-3-oxyl of claim 2 wherein R3 is CH3-, and R4 is
 5. The cis-2-(11-carboxy-3-undecenyl)-2-propyl oxazolidine-3-oxyl of claim 2 wherein R3 is CH3(CH2)2- and R4 is 